Microwave applicator and method of forming a microwave applicator

ABSTRACT

A method of forming a microwave applicator comprising forming a body comprising dielectric material so that there is a void in the dielectric material, and depositing conductive material in the void to form a feed for coupling energy into the dielectric material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, claims priority to and thebenefit of, U.S. Ser. No. 14/364,404 filed Jun. 11, 2014 entitled“MICROWAVE APPLICATOR AND METHOD OF FORMING A MICROWAVE APPLICATOR.” The'404 application is a U.S. national phase under 35 U.S.C. § 371 ofPCT/GB2012/053146 filed Dec. 14, 2012 and claims priority from GBApplication No. 1121436.8 filed Dec. 14, 2011. All of which areincorporated herein by reference in their entirety for all purposes.

FIELD OF THE INVENTION

This invention relates to a microwave applicator, a coupling for amicrowave applicator and to methods of fabricating a microwaveapplicator. The microwave applicator may comprise a disposableapplicator suitable for radiating microwave energy into a target for thepurposes of heating, such as surface tissue, for example skin or organsurfaces or any other material. The applicator of the invention may beused in medical microwave applications to treat or remove unwantedtissues or conditions affecting tissues.

BACKGROUND TO THE INVENTION

Microwave applicators employed to deliver energy in microwave heatingapplications are widely known. Often radiating elements are used tocouple the energy into the target to be heated. These radiating elementsare either probe-like antennas which are placed inside the heatingtarget or waveguide structures that contain the energy within theirinternal dielectric that interfaces with a surface of the target to passon the energy.

A number of these surface applicators exist, for example U.S. Pat. No.4,392,039 describes a dielectric heating applicator having a cylindricalmetal body filled with a mass of low loss dielectric material to be usedin direct contact with a body to form a resonant element creating aTM.sub.01 mode at the frequency of the applied microwave energy andhaving a dielectric filling of value greater than the target. Anotherexample is US 2008/0314894 which describes a dielectric heatingapplicator having a cylindrical metal body filled with a low lossdielectric material operating a TM.sub.01 mode to be used to launchmicrowave energy into tissue in direct contact with the applicator.

Many devices exist that couple or feed energy from electrical coaxialstructures into waveguide structures however the theory of transverseelectric (TE) and transverse magnetic (TM) mode launch techniques haslong been established in the literature as fundamental elements ofmicrowave components such as dielectric filled waveguides and dielectricloaded antennas.

Traditionally in any waveguide structure including dielectrically filledwaveguides a feed mechanism will include a coupling element (typically acoaxial centre conductor) which is placed into the waveguide to excite aparticular electromagnetic mode as supported by the waveguidedimensional properties, an example being U.S. Pat. No. 3,128,467. Inaddition to the waveguide properties the mode selection depends upon thegeometry of the coupling structure, for example an electrically groundedcoaxial loop creates a magnetic field that can be used to excite thetransverse electric (TE) mode, examples being U.S. Pat. Nos. 3,942,138and 3,128,467 and a radiating coaxial probe creates electric fields thatcan be used to selectively couple into the transverse magnetic (TM) modeexamples being U.S. Pat. Nos. 4,392,039 and 3,087,129. Although thesetechniques are well known there is novelty in the fabrication method tocreate these TE and TM mode coupling mechanisms by the current method.

In some applications it is desirable to physically reduce the dimensionsof a waveguide such as the cross-sectional area. As the operationalfrequency is related to the physical dimensions this can change thefrequency performance of the waveguide, with smaller cross-sectiontypically accommodating modes at higher frequencies. As it is oftendesired to maintain the same operational mode or frequency a commontechnique is to load the waveguide with a dielectric filling thusrestoring the operational frequency to the original position.

The coupling elements or structures are also placed into the dielectricmedium which is often a high dielectric electroceramic material. Thisnecessitates the machining of holes in the ceramic to accept the probesor conductive loops which can be expensive and impractical in highvolume manufacture.

Another limitation is that any air gap between a conductor and thedielectric can affect the microwave operating performance unless it hasbeen sufficiently accommodated in the design and controlled in themanufacture by tuning. Air gaps also allow the formation of high ordermodes and in high power applications can create a source of breakdowncausing arcing and burning of the ceramic or electrode. The effect ofair-gaps are particularly relevant if the Epsilon Relative (Er) value ofthe dielectric is much greater than that of the surrounding air (Er 1)such as in high dielectric ceramic Er 10, Er 20 Er 40 etc. In dielectricloaded waveguides the ceramic filling must be manufactured to a highaccuracy to ensure a good consistence of contact with the conductivewalls or stable dimensions of air filed regions to ensure accurateperformance. It is common practice to add tuning elements to negate theeffects of the air gaps created by manufacturing tolerances. This tuninginvolves the placement of capacitive or inductive elements such asmetallic or dielectric tuning materials to counteract the effects onperformance created by the air regions. This is often a time consumingand skilled process that dramatically increases the cost of the product.

One of the limitations of these types of dielectric filled waveguidelaunch mechanisms is the operational bandwidth of feed network istypically limited by the length of the coupling probes which operateover specific frequency ranges. This limitation can be improved by usingthe mismatch between the waveguide and the target to cancel with themismatch between the feed mechanism and the dielectric loaded waveguide.

Another factor is that coaxial microwave components require a conductiveelectrical attachment mechanism which usually takes the form of a pin(male) and socket (female). In the case of a dielectric waveguide feed apin or socket is placed within the dielectric material to facilitateconnection to an external coaxial feed. This arrangement is difficult tofabricate as most highly conductive metals are not compatible with thehigh temperatures present during the ceramic sintering process (typ.1300.degree. C.+) and would require to be added after the ceramic isfired, at which point the hardened ceramic is difficult and expensive tomachine.

Another factor in using pin/socket arrangements is that they possess afinite lifetime of connections becoming worn by repeated friction. Thisis a particular problem in microwave applications as small dimensionalchanges can have a detrimental effect upon microwave performance.

It is known to use self biasing pins (“pogo pin” or Z-pin) that canaccommodate repeated mating cycles in different technical areas, forexample as coaxial connections between a connector and circuit board asdescribed in U.S. Pat. No. 6,822,542 and as a plug component in acoaxial connector as can be found in U.S. Pat. No. 7,922,529.

In medical applications the cost of manufacture and lifetime of areusable part is of importance and it can be prohibitively expensive tocreate disposable microwave grade components for this market usingtraditional manufacture techniques such as bulk machining, drilling etc.

For microwave applicators manufactured using these methods a hole wouldhave to be machined into the ceramic material with a separate metallicpart being added to create the assembled component. This oftennecessitates a separate tuning mechanism or a number of iterations toensure that a reliable design is achieved. As this involves labour thisis an expensive method for mass production.

SUMMARY OF THE INVENTION

In a first aspect of the invention there is provided a method of forminga microwave applicator comprising forming a body comprising dielectricmaterial and depositing conductive material on the dielectric material.

The method may comprise forming the body so that there is a void in thedielectric material. The method may comprise introducing conductivematerial in the void, for example by depositing conductive material inthe void. The conductive material deposited in the void may be depositedsuch as to form a feed mechanism to couple energy into the dielectricmaterial.

The method may comprise performing a deposition process, for example acoating or plating process to deposit the conductive material on thedielectric material and/or in the void.

By depositing the conductive material it may be ensured that there is noair gap between the conductive and dielectric material. That caneliminate a requirement for additional tuning to compensate for any airgaps, as the air gaps do not exist and therefore their influence doesnot need to be accommodated in the design. That can substantially reducemanufacturing costs, and improve efficiency of operation.

The deposition process may comprise at least one of an ion vapourdeposition process, a sputtering process, a kiln co-fired ceramicplating process, a vacuum deposition process, an electroplating processor a solder reflow process. Alternatively or additionally a solidfilling can be employed to fill the void. The conductive material maycomprise at least one of silver, gold, nickel or an alloy thereof.

The use of a kiln co-fired process may ensure that a conductive pasteflows and adheres to a surface of the dielectric without an air gap.

The method may comprise depositing the conductive material so that thereis substantially no air gap between the dielectric material and theconductive material. The method may comprise depositing the conductivematerial so that the conductive material is in direct contact with thedielectric material.

The method may comprise substantially filling the void with theconductive material. That can provide a mechanical contact of greaterstrength or resilience for a contactor to touch.

The method may comprise forming the body using an injection mouldingprocess. The injection moulding process may comprise injection mouldingthe dielectric material. Thus, lower cost and more efficient manufacturemay be obtained, particularly when manufacturing large numbers ofapplicators.

The microwave applicator may be formed to be releasably attachableand/or detachable to a coupling for applying electromagnetic radiationto the applicator, for example for applying electromagnetic radiationvia the feed mechanism. The void and the conductive material may beconfigured so that, when the coupling is attached to the microwaveapplicator there is at least one substantially continuous electricallyconductive path between the coupling and the dielectric material via theconductive material. The at least one substantially continuouselectrically conductive path may comprise substantially no air gap.

The method may comprise depositing first conductive material on thesurface of the void, for example to create a hollow and/or thin wallconductor. The method may comprise depositing within the void secondconductive material of different type to the first conductive material.

The method may comprise depositing conductive material on an outersurface of the body, for example on an outer surface of the dielectricmaterial, for example to create a waveguide ground plane.

The method may comprise installing the body inside a holder.

The feed mechanism may comprise a TM mode feed, which may comprise forexample the conductively coated or filled void.

The feed mechanism may comprise the conductively coated or filled void,which may be configured to enter one plane and exit another, for exampleto link the or a conductor to the or a waveguide ground plane, which mayproduce a TE mode feed.

The method may comprise forming a conductive link from the conductivematerial deposited in the void to the conductive material deposited onthe outer surface. The conductive link may comprise a tab and/or mayaffect the frequency performance of the feed mechanism. The method maycomprise forming the conductive link by depositing conductive material,for example on an end face of the body. The depositing of the conductivematerial may comprise at least one of etching, patterning, printing,sputtering, vacuum deposition, ion vapour deposition.

The conductive link, for example the tab, may comprise a discontinuitywhich may act as a capacitive coupling. The capacitive coupling mayaffect the high frequency connection to the waveguide ground planeand/or may prevent a direct current (DC) path.

An electrical connection, for example the conductive link, may be usedto couple between a ground and a probe element on the outside of thestructure as opposed to placing them inside the ceramic. That can beachieved by the previously described coating methods or by using silkscreening to create specific geometries to avoid fully coating asurface.

In another independent aspect of the invention there is provided amethod of forming a coupling to a dielectrically filled microwaveapplicator comprising forming a feed probe electrical connection;forming a waveguide electrical connection, wherein the feed probeelectrical connection may be a connecting element that mechanically andelectrically contacts an applicator feed (or centre conductor) and thewaveguide electrical connection may be a connecting element thatmechanically and electrically contacts an outer surface (or waveguideground).

In a further independent aspect of the invention there is provided amethod of forming a microwave applicator comprising forming a firstwaveguide comprising first dielectric material, forming a secondwaveguide comprising second dielectric material and forming at least onefeed mechanism for coupling energy into the dielectric material into thefirst and/or second waveguide.

The first waveguide may be arranged to couple energy into the secondwaveguide or vice versa.

The first dielectric material may be different from the seconddielectric material and/or the first waveguide may be of a differentshape and/or size than the second waveguide.

The method may comprise forming the first waveguide and/or the secondwaveguide using an injection moulding process. The injection mouldingprocess may comprise injection moulding the first and/or seconddielectric material. The first dielectric material may be the same asthe second dielectric material. The method may comprise forming awaveguide body comprising a first section having a first shape and/orsize and a second section having a second shape and/or size. The firstsection may comprise or form part of the first waveguide and the secondsection may comprise or form part of the second waveguide. The waveguidebody may be formed by injection moulding the dielectric material into amould.

The first waveguide may be designed to communicate electromagneticenergy from the feed to the second waveguide by supporting anelectromagnetic mode.

The second waveguide may be configured to communicate electromagneticenergy from the first waveguide to the target.

The second waveguide may be configured to act as an impedancetransformer to transform a target impedance to that of the firstwaveguide.

The second waveguide may be configured to present a mismatch from atarget impedance to the first waveguide.

The second waveguide may be configured to present a mismatch to thefirst waveguide.

The first and second waveguide may be configured to present a mismatchto the feed mechanism to cancel a portion of the mismatch of the feedmechanism.

The first and second waveguides may be configured to present a mismatchto the feed mechanism that occurs at a frequency different to theoperating frequency of the feed mechanism thus increasing operatingbandwidth.

The method may comprise forming a plurality of waveguides, for exampleto provide a plurality of mismatches each occurring at a differentfrequency to provide increasing operating bandwidth. The method maycomprise forming the plurality of waveguides in a stepped structure.Each waveguide may have a different shape and/or size.

According to a further independent aspect of the invention there isprovided a microwave applicator comprising a body that comprisesdielectric material including a void in the dielectric material, andconductive material deposited in the void to form a feed for couplingenergy into the dielectric material.

The conductive material may comprise material deposited by a coating orplating process to deposit the conductive material on the dielectricmaterial.

There may be substantially no air gap between the dielectric materialand the conductive material. The conductive material may be in directcontact with the dielectric material.

The conductive material may be deposited on the surface of the void, forexample to create a hollow and/or thin wall conductor.

The applicator may comprise a second conductive material within the voidof a different type of material to the first conductive material.

The applicator may comprise conductive material on an outer surface ofthe body, for example on an outer surface of the dielectric material,which may form a waveguide ground plane.

The applicator may comprise a conductive link from the conductivematerial in the void to the conductive material on the outer surface.

The conductive link may comprise a tab. The conductive link may affectthe frequency performance of the feed mechanism.

The conductive link may comprise deposited conductive material. Theconductive link may comprise conductive material on an end face of thebody.

The conductive link may comprise a capacitive coupling.

The capacitive coupling may affect the high frequency connection to thewaveguide ground plane and/or may prevent a direct current (DC) path tothe waveguide ground plane.

The conductive link may include a discontinuity, which for exampleprovides the capacitive coupling.

The void may be substantially filled with conductive material. The bodymay be injection moulded. The dielectric material may be injectionmoulded.

The conductive material may comprise at least one of silver, gold,nickel or an alloy thereof.

The microwave applicator may be releasably attachable and/or detachableto a coupling for applying electromagnetic radiation to a waveguidecomponent of the applicator via the feed mechanism.

In a further aspect of the invention there is provided a plurality ofthe microwave applicators, each having different frequency transmissioncharacteristics, and each releasably attachable and/or detachable to thecoupling.

The void and the conductive material may be formed so that, when thecoupling is attached to the microwave applicator there is at least onesubstantially continuous electrically conductive path between thecoupling and the dielectric material via the conductive material.

The at least one substantially continuous electrically conductive pathmay comprise substantially no air gap.

The applicator may comprise a housing, and/or the microwave applicatormay comprise substantially no tuning components for tuning frequency.

The feed mechanism may comprise a TM mode feed.

The feed mechanism may be configured to enter one plane and exitanother, to link the conductive material to the or a waveguide groundplane.

According to a further, independent aspect of the present invention,there is provided an apparatus for use as a microwave applicatorcomprising:

a ceramic dielectric material;

at least one feed mechanism to couple energy into the ceramic material;

a waveguide to sustain an electromagnetic mode.

The ceramic dielectric material may be of any suitable form such asrectangular or cylindrical or any other shape that can support anelectromagnetic mode either propagating (radiating) or resonant (stored)and of any dielectric property value.

The ceramic dielectric material may be formed by being machined from abulk solid or by being injection molded, to contain holes (blind orpenetrating) or features to accept conductors required for a feedmechanism.

The feed mechanism may be formed by a plating or coating process such asion vapour depositing, sputtering or vacuum deposition of conductivemetals such as silver, gold, nickel or any other conductive metal tocoat the interior of the holes to create conductive features that adheredirectly to the surrounding dielectric material without air gap.

The feed mechanism may also be formed by depositing a metal in liquidstate such as silver, gold, nickel, solder or other conductive coatingor filling including any conductive metals, conductive epoxy compositesor conductive paints or coatings to cover the interior surface of theholes to create a conductive layer that adheres directly to thedielectric material without air gap. The conductive material depthshould be substantial enough to accommodate the required electromagneticskin depth to support surface electrical currents at microwavefrequencies.

The conductive material may be applied to the interior surface only tocreate a hollow “thin wall” conductor or may be applied in single ormultiple applications to partially or entirely fill the void of the holeto create a solid conductor.

Separately a secondary conductive filling of a different material may beintroduced to join with the primary “thin wall” conductor to entirelyfill the void to create a solid conductor.

The outer surfaces of the ceramic component may be coated in aconductive material to generate the waveguide ground plane negating therequirement for a conductive holder or alternatively negating therequirement for applying a conductive foil jacket to support thewaveguide mode. A conductive or insulating support holder may also beused in conjunction with this technique to enhance the mechanicalstrength if required. Where there are transitions in diameter in theouter walls these may be tapered to improve the adhesion of the metalliccoating to the surface.

The feed mechanism may comprise a conductively coated or filled blindhole to create a TM mode feed probe.

It may also be a conductively coated or filled penetrating hole thatenters one face and exits another to create a path between the centreconductor and the waveguide ground plane to create a TE mode feed.

In particular embodiments, the TE mode feed may be connected directly tothe waveguide ground plane via a conductive body or “tab” patterned,etched, printed or deposited onto the end face surface of the ceramicwaveguide containing the feed probe.

The tab may be of any length or shape that may affect the frequencyperformance of the feed mechanism.

The tab may be connected directly to the feed probe or may have adiscontinuity along its length acting as a capacitive coupling effectingthe high frequency connection to the waveguide ground plane.

According to a further independent aspect of the present invention thereis provided an apparatus for use in coupling to a dielectrically filledmicrowave applicator comprising:

a feed probe electrical connection;

a waveguide electrical connection.

The feed probe electrical connection may be a connecting element thatmechanically and electrically contacts to the applicator feed.

The waveguide electrical connection may be a connecting element thatmechanically and electrically contacts the applicator waveguide (alsocalled the outer body or waveguide ground).

The feed probe electrical connection may be formed by a self biasingpin, conductive spring, conductive elastomer or other self biasingelectrical contact. A pogo pin such as a MILL-MAX 0906 Spring-LoadedPogo Pin may be used for example. The use of a self-biasing pin toconnect to a dielectric waveguide feed in a microwave applicator canprovide a quick, reliable connection to the microwave applicator withoutexcessive connect/disconnect forces, and can enhance connection lifetimewhilst accommodating manufacturing tolerances.

The waveguide electrical connection may be formed by a conductive sleevethat accepts the waveguide and makes electrical contact with theconductive outer coating of the waveguide. The sleeve could comprise anarray of sprung contactors arranged to accommodate a waveguide beinginserted and able to accommodate manufacturing and alignment tolerancesby being flared.

At least part of the waveguide electrical connection device may befabricated from heat treated brass, beryllium copper, or anotherhardened metal and may be coated with gold, silver or nickel to ensuregood long-term electrical contact.

According to a further, independent aspect of the present inventionthere is provided an apparatus for use as a microwave applicatorcomprising.

a ceramic dielectric material;

at least one feed mechanism to couple energy into the ceramic material;

a first waveguide to sustain an electromagnetic mode.

a second waveguide region of different dimension to the first

The feed mechanism may be designed to couple energy into the firstwaveguide.

The first waveguide may be designed to communicate electromagneticenergy from the feed to the second waveguide by supporting anelectromagnetic mode.

The second waveguide may be designed to communicate electromagneticenergy from the first waveguide to the target.

The second waveguide may be designed to act as an impedance transformerto transform the target impedance to that of the first waveguide.

The second waveguide may be designed to present a mismatch from thetarget impedance to the first waveguide.

The second waveguide may be designed to present a mismatch to the firstwaveguide.

The first and second waveguide may be designed to present a mismatch tothe feed mechanism to cancel a portion of the mismatch of the feedmechanism.

The first and second waveguide may be designed to present a mismatch tothe feed mechanism that occurs at a frequency different to the operatingfrequency of the feed mechanism to enhance the operating bandwidth.

A number of waveguide steps of various dimensions may be employed usingthe aforementioned technique to provide a plurality of mismatches each adifferent frequency corresponding to each waveguide dimension to provideincreased operating bandwidth.

In another independent aspect of the invention there is provided amicrowave applicator comprising:

a dielectric material containing a void;

a conductive filling introduced into the void to create a feed mechanismto couple energy into the dielectric material; and

a waveguide region to sustain an electromagnetic mode.

The dielectric material may be of any regular shape such as rectangularor cylindrical or any other shape supporting an electromagnetic mode ofeither propagating (radiating) or resonant (stored) where the dielectricmaterial is of any dielectric property value.

The dielectric material may be formed by being machined or injectionmolded to contain a void such as a hole (blind or penetrating).

The feed mechanism may be formed by a plating or coating process such asion vapour depositing, sputtering or vacuum deposition of conductivemetals such as sliver, gold, nickel or other conductive metals to coatthe interior of the void creating a conductive feature that adheresdirectly to the surface of the dielectric material without air gap.

The feed mechanism may be formed by depositing a metal in liquid statesuch as silver, gold, nickel, solder or other conductive coating orfilling including any conductive metals, conductive epoxy composites orconductive paints or coatings.

The deposited conductive material thickness may accommodate the requiredelectromagnetic skin depth to support surface electrical currents atmicrowave frequencies.

The conductive material may be applied to the interior surface to createa hollow “thin wall” conductor.

The conductive material may be applied in single or multipleapplications to partially or entirely fill the void of the hole tomanufacture a solid conductor.

A secondary conductive filling of different type may be applied to joinwith the primary “thin wall” conductor to entirely fill the void tocreate a solid conductor.

The outer surfaces of the dielectric material may be coated by a platingor coating process such as ion vapour deposition, sputtering or vacuumdeposition of conductive metals such as silver, gold, nickel or otherconductive metals to adhere directly to the outer surface of thedielectric material without air gap to create a waveguide ground plane.

The microwave applicator may be installed inside a conductive orinsulating support holder to enhance mechanical strength.

The feed mechanism may comprise a conductively coated or filled blindhole creating a TM mode feed.

The feed mechanism may comprise a conductively coated or filledpenetrating hole that enters one plane and exits another to link thecentre conductor to the waveguide ground plane to produce a TE modefeed.

The link to the waveguide ground plane may be via a conductive body or“tab” patterned, etched, printed or deposited onto the end face surfaceof the waveguide containing the feed probe. The tab may be of any lengthor shape that effects the frequency performance of the feed mechanism.

The tab may have a discontinuity along its length acting as a capacitivecoupling effecting the high frequency connection to the waveguide groundplane and preventing a direct current (DC) path.

In a further independent aspect of the invention there is provided acoupling means to a dielectrically filled microwave applicatorcomprising:

a feed probe electrical connection;

a waveguide electrical connection;

wherein the feed probe electrical connection may be a connecting elementthat mechanically and electrically contacts the applicator feed (orcentre conductor) and the waveguide electrical connection may be aconnecting element that mechanically and electrically contacts the outersurface or (waveguide ground)

The feed probe electrical connection may be formed by a self biasingpin, conductive spring, conductive elastomer or other self biasingelectrical contact.

The waveguide electrical connection may be formed by a conductive sleeveto accept the waveguide and make electrical contact with the conductiveouter surface of the waveguide.

An array of sprung contactors may be arranged to accommodate thewaveguide being inserted capable of accommodating manufacturing andalignment tolerances by being flared.

The waveguide electrical connection device may be fabricated from heattreated brass, beryllium copper, or another hardened metal and coatedwith gold, silver or nickel.

In another independent aspect of the invention, there is provided amicrowave applicator comprising

a dielectric material;

at least one feed mechanism to couple energy into the dielectricmaterial;

a first waveguide containing dielectric material to sustain anelectromagnetic mode;

a second waveguide region containing dielectric material of differentdimension to the first. The microwave applicator may possess a feedmechanism designed to couple energy into the first waveguide.

The first waveguide may be designed to communicate electromagneticenergy from the feed to the second waveguide by supporting anelectromagnetic mode.

The second waveguide may be designed to communicate electromagneticenergy from the first waveguide to the target.

The second waveguide may be designed to act as an impedance transformerto transform the target impedance to that of the first waveguide.

The second waveguide may be designed to present a mismatch from thetarget impedance to the first waveguide.

The second waveguide may be designed to present a mismatch to the firstwaveguide.

The first and second waveguides may be designed to present a mismatch tothe feed mechanism to cancel a portion of the mismatch of the feedmechanism.

The first and second waveguides may be designed to present a mismatch tothe feed mechanism that occurs at a frequency different to the operatingfrequency of the feed mechanism thus increasing operating bandwidth.

A number of waveguide steps of various dimensions may be employed toprovide a plurality of mismatches each occurring at a differentfrequencies corresponding to each waveguide dimension to provideincreasing operating bandwidth.

There may also be provided an apparatus or method substantially asdescribed herein with reference to the accompanying drawings.

Any feature in one aspect of the invention may be applied as a featurein any other aspect of the invention, in any appropriate combination.For example, apparatus features may be applied as method features andvice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described,by way of example only, with reference to the accompanying figures, inwhich:

FIG. 1 illustrates a series of diagrammatic cross sectional views of theceramic plating process;

FIG. 2 shows diagrammatic cross sectional views of electric and magneticcoupling feeds realizable in hollow plated and filled platedconfigurations;

FIG. 3 is a number of diagrammatic cross sectional views of magneticcoupling feed configurations;

FIG. 4 illustrates diagrammatic cross sectional views of electriccoupling feed configurations;

FIG. 5 shows a photograph of a cross section of an embodiment of aplated probe inside a ceramic body;

FIG. 6 shows a diagrammatic illustration of self biasing pin contactinga plated magnetic coupling probe feed arrangement;

FIG. 7 shows diagrammatic cross sectional views of the effect ofmultiple steps in the ceramic waveguide on performance bandwidth;

FIG. 8 illustrates diagrammatic cross sectional views of variouswaveguide width transitions;

FIG. 9 displays a diagrammatic isometric view of a cross section of anembodiment of a microwave applicator.

FIG. 10 displays a diagrammatic view of the external plating on anembodiment of a microwave applicator.

FIG. 11 displays a dimensioned drawing of the ceramic microwaveapplicator part.

FIG. 12 displays the simulated results for an embodiment of themicrowave applicator when placed against simulated tissue.

FIG. 13 displays the measured results for an embodiment of the microwaveapplicator when placed against tissue;

FIG. 14 displays a dimensioned drawing of the assembled disposablemicrowave applicator part; and

FIG. 15 displays a dimensioned drawing of the assembled reusable handpiece which connects to the microwave applicator part.

DETAILED DESCRIPTION

Certain embodiments as disclosed herein provide for a microwaveapplicator that incorporates a probe feed for the transmission of energyfrom a coaxial feed into a dielectric filled waveguide and ultimatelyinto a target.

Various arrangements are provided in the different embodiments, afterreading the description, it will become apparent to one skilled in theart that various changes and modifications can be made, and equivalentsor alternative embodiments employed. However, although variousembodiments of the present invention will be described herein, it isunderstood that these embodiments are presented by way of example onlyand should not be construed to limit the scope or breadth of the presentinvention as set forth in the appended claims.

With reference initially to FIG. 1 of the drawings, there are describedprocess steps required to fabricate a probe from a dielectric body 1.

In the embodiment of FIG. 1, the dielectric probe is formed using aninjection moulding process. Any other suitable method for forming thebody can be used in other embodiments.

A void 2 is initially introduced into the dielectric body. The void 2 inthe embodiment of FIG. 1 is formed as part of the injection mouldingprocess, but in alternative embodiments the void be formed by drilling,erosion, or any other suitable forming technique.

A conductive coating, covering or plating 3 is introduced to the outsidesurface of the dielectric body to act as an electromagnetic waveguide.The conductive coating, covering or plating can function as a waveguideground plane, depending on the configuration of the device in use. Aconductive coating, covering or plating is also deposited onto theinterior surface of the void to create a hollow conductor 4. In theembodiment of FIG. 1 the conductive material is gold, but any suitableconductive material can be used in other embodiments, for examplesilver, gold, nickel or an alloy thereof.

In the embodiment of FIG. 1, the conductive coating is deposited ontothe interior surface of the void and onto the outside surface of thedielectric body using a kiln co-fired ceramic plating process. Insubsequent operation, the hollow conductor 4 effectively acts like aprobe that can be used to launch electromagnetic waves into the ceramicwaveguide.

It is a feature of the embodiment of FIG. 1 that the conductive materialdeposited into the void to form the hollow conductor 4 is deposited sothat there is substantially no air gap between the dielectric materialand the conductive material and data material is in direct contact withthe dielectric material.

In applications where a TE mode is to be launched a known method is toemploy a magnetic coupling, realised by shorting the centre conductor tothe waveguide wall. In the embodiment of FIG. 1, this is achieved byproviding a connection 5 comprising conductive material between thehollow conductor 4 and the conductive material providing the waveguidewall 3. An electrically conductive material is painted, coated, silkscreened, etched or deposited by any suitable method onto the end faceof the dielectric body 1 to create the connection 5.

In the embodiment of FIG. 1, the connection 5 comprises a tab thatincludes a conductive discontinuity that provides capacitive couplingbetween the conductive material deposited in the void and the conductivematerial deposited on the outer surface. In this case, the capacitivecoupling in operation affects the high frequency connection to thewaveguide ground plane provided by the conductive material 3 on theouter surface of the dielectric material, and/or prevents a directcurrent (DC) path to the waveguide ground plane.

In final stages of manufacture of the dielectric body is installed in anouter housing, also referred to as a holder, formed for example ofplastic, which provides an insulating arrangement around the outerconductive layer 3. In the embodiment of FIG. 1, the resulting microwaveapplicator is a disposable component for medical applications that canbe provided for single-use or a limited number of uses. The applicatorin this case can be connected to a probe feed apparatus in turncomprising or connected to a microwave source. The applicator in thisembodiment does not include any frequency tuning components and tuning,if any, can be performed by tuning components of the separate probe feedapparatus or microwave source. By limiting the components included inthe microwave applicator (in the case of FIG. 1 to a dielectric body,deposited conductive material and an outer housing) and by usingtechniques such as injection moulding and deposition processes, aparticularly efficient method of mass producing or otherwisemanufacturing microwave applicators can be provided.

In the embodiment of FIG. 1, each of the regions 3, 4, 5 of conductivematerial can be deposited in a single deposition process, formanufacturing efficiency, if so desired, but often the depositionprocess will be repeated to deposit the different regions.

The conductor thickness can be selected in dependence upon currentcarrying requirements and operating frequency. The conductive coatingcan be formed to be continuous and to not contain holes or excessivelythin regions to avoid electrical breakdown (sparking).

To fulfil other requirements such as supporting higher currents, ormechanical connection it can be desirable to fill the hollow conductor 4with a conductive or other filling 6, as shown schematically in FIG. 1.The conductive filling 6 can be of the same or different material to thematerial of the deposited layer 4. The materials can be selected toprovide desired electromagnetic and mechanical characteristics.

It will be understood that embodiments are not limited to the particulararrangement shown in FIG. 1. FIG. 2 shows microwave applicators 7, 8, 9,10, 12, 13 in various other embodiments, namely a coated probe 7, filledcoated probe 8, shorted coated probe 9, shorted filled coated probe 10,coated conductive loop 12 and filled coated conductive loop 13. In eachcase, dielectric material is shown by hatched areas and conductivematerial is shown by solid black areas.

The conductive link between the void conductive material and theconductive material on the outer surface is not limited to thearrangement of FIG. 1 and any suitable conductive link can be used. Asmall number of possible conductive links in the form of magnetic feedcoupling configurations in alternative embodiments are illustrated inFIG. 3, for example an end-coupled probe 14, side-coupled probes 15, 17,loop 18 and T bar-coupled probe 16. In FIG. 3, the boundary of thedielectric material is shown by the rectangular shape and the conductivelink is shown by solid black areas. The outer conductive coating is notshown for clarity but would be present along each of the long sides ofthe rectangular shape.

In FIG. 4 various configurations of the void filled with conductivematerial forming an electric probe, according to alternativeembodiments, are shown, namely a standard probe 19, top-hat probe 20,and spherically-tipped probe, 21. The conductive material within thevoid is again shown by solid black areas and the boundary of thedielectric material is shown by the rectangular shape.

A photograph of a cross section of an embodiment of a plated probe isdisplayed in FIG. 5. In this image the probe void has been molded intothe surrounding dielectric 22. A conductive silver plating 23 has beenintroduced onto the interior walls of the void to form a hollow probe.This plating or coating is at least 80 microns in depth as theelectrical skin depth at 8 GHz is 72 microns for pure Silver(resistivity=1.59.mu.OMEGA.-cm).

FIG. 6. shows an embodiment of a connection means between a coaxial feedline and a shorted probe feed. In this embodiment a MILL-MAX 0906Spring-Loaded Pogo Pin 24 contacts against a plated probe 25incorporating a rectangular connection tab 26 that provides an electriccontact between the probe and the conductive outer waveguide wall. Inthis instance the spring loaded pin is surrounded by air as part of thecoaxial to waveguide transition.

With reference to FIG. 7, the effect of various waveguide steps upon theoperating bandwidth is described. The target 27 to which electromagneticradiation is to be applied may be any dielectric material such as tissueor a material having a dielectric different to the dielectric of thewaveguide. The difference in dielectric creates a mismatch 28. Theimpedance seen by the feed 29 will partially cancel with the mismatch 28to create a narrow operating bandwidth 30, centred upon a frequency ofoperation (fo) with an upper and lower band (−f, +f) which possesses areturn loss or “match” typically better that −12 dB between thesepoints. The operating frequency (fo) is related to the length of theprobe and the dielectric constant of the waveguide having dimension tosupport the chosen mode at the required frequency. Out-with the (−f, +f)frequency ranges all the incident energy is returned back into the feedmechanism and reflected back to the source. By adding another waveguidedimension a further mismatch 31 can be introduced that will partiallycancel with the impedance seen by the feed 29. This cancellation can beselected to occur at a frequency f2 different to first f1 to result inan increased operating bandwidth 32. Likewise by adding other waveguidedimensions further mismatches 33 can be created to enhance the operatingbandwidth 34.

It should be noted that “waveguide dimension” may refer to a new portionwith different diameter, height, width, shape, material or dielectricconstant than that of the existing waveguide. It may also refer toremoving or adding material to the existing waveguide such as creating avoid or hole in the material or in the conductive walls or adding aconductive or dielectric material into, or onto the existing waveguideto manufacture a discontinuity to create the mismatch(s).

In the case where a single dielectric material is used, for example asingle one-piece dielectric body, various embodiments of possibletransitions are illustrated in FIG. 8. These transitions are applicableto any shape of waveguide such as cylindrical, rectangular, elliptical,reduced height etc. and may be stepped 35, tapered 36, curved inwards 37or curved outwards 38. It has been found that the use of a taper orcurved profile, particularly when used in conjunction with a depositionprocess to deposit conductive material, is to reduce variation in thedensity or thickness of conductive material at or around the location oftransition as such variation can increase the effective dielectricconstant of the part. Thus, the use of a taper or curved profile can insome embodiments reduce variation or inaccuracy in electromagneticproperties. A microwave applicator for use in depositing energy intotissue according to an embodiment of the present invention isillustrated in FIG. 9. In this example a high dielectric ceramic (D37™by Morgan Electroceramic Ltd.) was constructed with an upper waveguide39 of length 5.3 mm and diameter 6.8 mm connected via a 2 mm taperedsection to a lower waveguide 40 of length 9.2 mm and diameter 4.75 mm.The waveguide is placed into a receptacle 41 which maintains electricalcontinuity to the waveguide ground plane using a cylindrical arrangementof sprung metallic fingers, flared to accept the ceramic body. To reducethe cost of manufacture the receptacle 41 is designed to cap the launchmechanism and contains all the highest tolerances in one component.

The internal probe 43 of length 2.5 mm and diameter 1 mm was silverplated and loaded with lead free solder to provide a mechanical deadstop for a MILL-MAX 0906 Spring-Loaded Pogo Pin 42. FIG. 10 illustratesthe external plating of the ceramic component where a conductive silverplating was applied to the outer surface 44 to create the waveguide anda 1 mm wide by 3.375 mm length rectangular tab 45 is screen printed ontothe lower end face to electrically short the probe to the outerwaveguide ground plane for the purpose of launching a transverseelectric (TE) mode.

FIG. 12 illustrates the designed microwave performance of thearrangement when placed against tissue for operation at 8 GHz withgreater than 150 MHz operating bandwidth. Finally, FIG. 13 is a graphrepresenting testing results for the arrangement confirming theoperation as designed.

FIG. 14 is a dimensioned drawing of an assembled disposable microwaveapplicator part according to an embodiment. FIG. 15 is a dimensioneddrawing of an assembled reusable hand piece which connects to themicrowave applicator part of FIG. 14.

In the embodiment of FIG. 1, the conductive material is deposited ontothe dielectric body using a kiln co-fired ceramic plating process.However, in alternative embodiments, any other suitable depositionmethod can be used, for example an ion vapour deposition process, asputtering process, or a vacuum deposition process. In such alternativeembodiments, the conductive material can be deposited into the void andonto the outer surfaces in a single process or, alternatively, thematerial can be deposited into the void and onto the outer surfacesusing different techniques and/or at different stages of the process.

Embodiments can include plating, metalizing or filling of molded voidsin particular blind voids to create microwave coupling structures inparticular within ceramic dielectrics. The conductive coating of blindvoids may be provided.

By using new manufacture techniques in conjunction with innovativemicrowave design, a cost effective high volume disposable microwaveapplicator can be realised.

It should be understood that the embodiments described herein are merelyexemplary and that various modifications may be made thereto withoutdeparting from the scope of the invention.

Each feature disclosed in the description, and (where appropriate) theclaims and drawings may be provided independently or in any appropriatecombination.

1. A microwave applicator comprising a body that comprises dielectricmaterial including a void in the dielectric material, and conductivematerial deposited in the void to form a feed for coupling energy intothe dielectric material.
 2. The microwave applicator according to claim1, wherein the conductive material adheres to the dielectric material ofthe surface of the void over substantially all of the surface of thevoid.
 3. The microwave applicator according to claim 1, that comprises awaveguide comprising the dielectric material, wherein the microwaveapplicator is attachable to a coupling for applying electromagneticradiation to the waveguide via the feed, and the conductive materialadheres to the dielectric material of the surface of the void and formsthe feed for applying the electromagnetic radiation to the waveguide. 4.The microwave applicator according to claim 1, wherein there issubstantially no air gap between the dielectric material and theconductive material.
 5. The microwave applicator according to claim 1,comprising first conductive material deposited on the surface of thevoid to create at least one of a hollow conductor or thin wallconductor.
 6. The microwave applicator according to claim 5, comprisingsecond conductive material deposited within the void and of differenttype to the first conductive material.
 7. The microwave applicatoraccording to claim 1, comprising conductive material deposited on anouter surface of the body and forming a waveguide ground plane.
 8. Themicrowave applicator according to claim 7, comprising a conductive linkfrom the conductive material deposited in the void to the conductivematerial deposited on the outer surface.
 9. The microwave applicatoraccording to claim 8, wherein at least one of: a. the conductive linkcomprises a tab; b. the conductive link affects the frequencyperformance of the feed; c. the conductive link comprises conductivematerial deposited on an end face of the body; d. the conductive linkincludes a capacitive coupling; e. the conductive link includes acapacitive coupling that affects a high frequency connection to thewaveguide ground plane or prevents a direct current (DC) path to thewaveguide ground plane; or f. the conductive link includes adiscontinuity.
 10. The microwave applicator according to claim 1,wherein at least one of: a. the void is substantially filled with theconductive material; or b. the conductive material comprises at leastone of silver, gold, nickel or an alloy thereof.
 11. The microwaveapplicator according to claim 1, which comprises a waveguide and whichis at least one of releasably attachable and releasably detachable to acoupling for applying electromagnetic radiation to the waveguide via thefeed.
 12. The microwave applicator according to claim 1, which comprisessubstantially no tuning components for tuning frequency.
 13. Themicrowave applicator according to claim 1, wherein at least one of: a.the feed comprises a TM mode feed; or b. the feed is configured to enterone plane and exit another, to link the conductive material to awaveguide ground plane.